1. Field of the Invention
The present invention relates to a technique of simulating the condition of traffic in a road network.
2. Description of the Related Art
Road traffic control systems are designed, generally for controlling the traffic in accordance with the actual traffic of many vehicles running on the roads. In any road network, the roads and traffic facilities must be changed or new roads and new facilities must be built, in order to eliminate traffic congestion or to ensure a smooth traffic flow on a road. However, traffic congestion may occur on other roads or the traffic flow on other roads may become less smooth.
In view of this, the traffic control plan must be verified or quantitatively evaluated for its effect. The traffic simulation technique is therefore very important. Since traffic simulation evaluates the traffic control and predicts the traffic conditions on various roads, it can help to plan an effective traffic control system.
Traffic simulation methods are classified into two types, i.e., macrosimulation method and microsimulation method. In the macrosimulation method, the traffic of vehicles is regarded as a continuous fluid flow, as described in, for example, Easy Traffic Simulation, Japan Society of Traffic Engineering, Maruzen Co., Ltd., June 2006, ISBN 4-905990-31-9C3051. The reference describes a traffic simulation technique that utilizes a block density method to predict the traffic congestion on highways.
In the microsimulation method, the behavior of each vehicle on a specific road is first simulated, the results of simulation are then accumulated for the respective time periods, and the traffic flow of the vehicles is reproduced on a road model, as described in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2004-258889. This reference discloses a traffic simulator that uses molecular dynamics, which is usually applied in the fields of physics and material studies. The traffic simulator describes the influence each vehicle imposes on any nearby vehicle, as a potential hazard, and reproduces and displays the behavior of the vehicle.
In the macrosimulation method, the calculation load on the computer used is smaller than in the microsimulation method. In the microsimulation method, the calculation load on the computer is large because a calculation must be performed to simulate, as pointed out above, the behavior of each vehicle. The macrosimulation method, in which the calculation load on the computer is small, is now used in most cases to design a road network.
To design a road network for a broad area, it is necessary to predict traffic congestion, which more influences the traffic condition than anything else. Traffic congestion results from, in many cases, the drivers' lane changing at junctions or strange behavior of individual vehicles. The traffic simulator that performs the macrosimulation method defines the roads existing in each road-network section as links, and processes the traffic data (average value) averaged for each link. Further, the traffic simulator uses not only the average data for each link, but also the data actually acquired by a plurality of vehicle sensors provided along the roads, reproducing the traffic condition and predicting a traffic condition. The traffic simulator then displays the reproduced traffic condition and the predicted traffic condition on a display screen.
However, the traffic simulator performing the macrosimulation method cannot simulate the behavior of each vehicle or process the various aspects of behavior, to achieve microscopic reproduction of traffic congestion. Consequently, with any traffic simulator that performs the macrosimulation method it is not always easy to reproduce or predict traffic congestions.